1. Field
The present invention relates to LED drivers, and more particularly to off-line LED drivers with integrated synthesized digital optical feedback.
2. Related Art
Capacitive drop off-line LED drivers are known (On Semiconductor Application Note AND8146/D). However, this non-isolated driver has low efficiency, delivers relatively low power, and delivers a constant current to the LED but with no temperature compensation, no dimming arrangements, and no protection for the LED.
A few isolated off-line LED drivers are known:                With line frequency transformer and current regulator, On Semiconductor Application Note AND 8137/D;        Off-line LED driver with NCP1014P100 current mode controller, On Semiconductor Application Note AND8136/D;        White LED luminary Light Control System, U.S. Pat. No. 6,441,558;        LED Driving Circuitry with Light Intensity Feedback to Control Output Light Intensity of an LED, U.S. Pat. No. 6,153,985;        Non-Linear Light-Emitting Load Current Control, U.S. Pat. No. 6,400,102;        Flyback as LED Driver, U.S. Pat. No. 6,304,464;        Power Supply for LED, U.S. Pat. No. 6,557,512; and        Voltage Booster for Enabling the Power Factor Controller of a LED Lamp Upon Low AC or DC Supply, U.S. Pat. No. 6,091,614.        
These drivers in general are too complicated as they use secondary side signals which have to be coupled with the controller on the primary side across the isolation.
For a high quality optical system multiple LED system parameters may be measured, which makes almost impossible the technical task of taking these signals across the safety isolation to feed controllers which reside on the primary side.